// ThreadPool.h
#pragma once
#include <vector>
#include <queue>
#include <thread>
#include <mutex>
#include <condition_variable>
#include <future>
#include <functional>
#include <atomic>

class ThreadPool {
public:
    ThreadPool(size_t);
    ~ThreadPool();

    template<class F, class... Args>
    auto enqueue(F&& f, Args&&... args) 
        -> std::future<typename std::result_of<F(Args...)>::type>;

private:
    std::vector<std::thread> workers;
    std::queue<std::function<void()>> tasks;

    std::mutex queue_mutex;
    std::condition_variable condition;
    std::atomic<bool> stop;
};

// 构造函数
inline ThreadPool::ThreadPool(size_t threads)
    : stop(false)
{
    for(size_t i = 0; i < threads; ++i)
        workers.emplace_back([this] {
            while(true) {
                std::function<void()> task;
                {
                    std::unique_lock<std::mutex> lock(this->queue_mutex);
                    this->condition.wait(lock, [this]{ return stop || !tasks.empty(); });
                    if(stop && tasks.empty()) return;
                    task = std::move(tasks.front());
                    tasks.pop();
                }
                task(); // 执行任务
            }
        });
}

// 添加任务
template<class F, class... Args>
auto ThreadPool::enqueue(F&& f, Args&&... args) 
    -> std::future<typename std::result_of<F(Args...)>::type>
{
    using return_type = typename std::result_of<F(Args...)>::type;

    auto task = std::make_shared< std::packaged_task<return_type()> >(
        std::bind(std::forward<F>(f), std::forward<Args>(args)...)
    );
    
    std::future<return_type> res = task->get_future();
    {
        std::unique_lock<std::mutex> lock(queue_mutex);
        if(stop) throw std::runtime_error("enqueue on stopped ThreadPool");
        tasks.emplace([task](){ (*task)(); });
    }
    condition.notify_one();
    return res;
}

// 析构函数
inline ThreadPool::~ThreadPool()
{
    stop = true;
    condition.notify_all();
    for(std::thread &worker: workers)
        worker.join();
}
